Add Page Box layer for C7 class optimization

- Implement tiny_page_box.c/h: per-thread page cache between UC and Shared Pool
- Integrate Page Box into Unified Cache refill path
- Remove legacy SuperSlab implementation (merged into smallmid)
- Add HAKMEM_TINY_PAGE_BOX_CLASSES env var for selective class enabling
- Update bench_random_mixed.c with Page Box statistics

Current status: Implementation safe, no regressions.
Page Box ON/OFF shows minimal difference - pool strategy needs tuning.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

core/hakmem_tiny_publish_box.inc

@@ -5,6 +5,11 @@
 // TLS hint: last adopted SuperSlab/slab to avoid rescans
 #include "tiny_sticky.h"
 
+// Tiny Page Box: C5〜C7 用 Tiny-Plus page pool（Superslab/Warm Pool より前段の箱）
+// tiny_tls_bind_slab() で新しい TLS Slab が bind されたタイミングで
+// tiny_page_box_on_new_slab() を呼び出し、Page Box 側の page pool を更新する。
+#include "box/tiny_page_box.h"
+
 // Mailbox box
 #include "box/mailbox_box.h"
 
@@ -363,6 +368,9 @@ static inline void tiny_tls_bind_slab(TinyTLSSlab* tls, SuperSlab* ss, int slab_
     tls->slab_idx = (uint8_t)slab_idx;
     tls->meta = &ss->slabs[slab_idx];
     tls->slab_base = tiny_slab_base_for(ss, slab_idx);
+
+    // Tiny Page Box にも新しい slab を通知しておく（C7 など有効クラスのみ）
+    tiny_page_box_on_new_slab(tls);
 }
 
 static inline uint32_t tiny_tls_default_refill(uint32_t cap) {